Q: blue and white horizontal lines appear at startup, the computer doesn't start up past this. Anyy suggestions?

What model iMac? What does "About this Mac" report for your processor type?

Query by serial number

Apple's warrenty database will identify the type of Mac you have.  Your serial number is securely sent.  Provides more information for newer machines.

https://selfsolve.apple.com/agreementWarrantyDynamic.do

This site provides more information.  Best for older machines.  Note, serial number is sent in the clear.

"A serial number is a unique, identifying number or group of numbers and letters assigned to an individual piece of hardware or software. It's used for various things depending on the product / brand but what is your Mac's serial number for and more importantly... what is it hiding and what can it do for you ?"

http://www.appleserialnumberinfo.com/Desktop/index.php

or

This site provides more information, but lacks security too.

"A serial number is a unique, identifying number or group of numbers and letters assigned to an individual piece of hardware or software. It's used for various things depending on the product / brand but what is your Mac's serial number for and more importantly... what is it hiding and what can it do for you ?"

http://www.appleserialnumberinfo.com/Desktop/index.php

http://www.chipmunk.nl/klantenservice/applemodel.html

    ( hint by K Shaffer  )